Nils O. Selåsdal
59 lines
1.5 KiB
C
59 lines
1.5 KiB
C
#include <assert.h>
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#include "ucore/ticket_lock.h"
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//pthread implementation of http://en.wikipedia.org/wiki/Ticket_lock
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//The underlying phtread mutex is not held while the lock is acquired.
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//This will allow other threads to enqueue itself.
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//
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//The condition variable is needed to wake up threads waiting to acquire
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//the lock instead of letting the system block on the pthread mutex while waiting.
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int uc_ticket_lock_init(struct UCTicketLock *lock)
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{
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return uc_ticket_lock_init_ex(lock, NULL, NULL);
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}
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int uc_ticket_lock_init_ex(struct UCTicketLock *lock,
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pthread_mutexattr_t *mattr,
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pthread_condattr_t *cattr)
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{
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int rc;
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lock->queue_head = 0;
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lock->queue_tail = 0;
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rc = pthread_mutex_init(&lock->mutex, mattr);
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assert(rc == 0);
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if (rc != 0) {
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return rc;
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}
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rc = pthread_cond_init(&lock->cond, cattr);
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if (rc != 0) {
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pthread_mutex_destroy(&lock->mutex);
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}
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assert(rc == 0);
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return rc;
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}
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void uc_ticket_lock(struct UCTicketLock *lock)
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{
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unsigned long queue_me;
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pthread_mutex_lock(&lock->mutex);
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queue_me = lock->queue_tail++;
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while (queue_me != lock->queue_head)
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{
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pthread_cond_wait(&lock->cond, &lock->mutex);
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}
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pthread_mutex_unlock(&lock->mutex);
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}
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void uc_ticket_unlock(struct UCTicketLock *lock)
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{
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pthread_mutex_lock(&lock->mutex);
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lock->queue_head++;
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pthread_cond_broadcast(&lock->cond);
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pthread_mutex_unlock(&lock->mutex);
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}
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